Re: [PATCH] x86: adjust which Dwarf2 register numbers to use

[Jan Beulich <jbeulich@suse.com>]

On 15.02.2024 23:22, Indu Bhagat wrote:
> On 2/9/24 00:11, Jan Beulich wrote:
>> Consumers can't know which execution mode is in effect for a certain
>> piece of code; they can only go from object file properties. Hence which
>> register numbers to encode ought to depend solely on object file type.
>>
>> --- a/gas/config/tc-i386.c
>> +++ b/gas/config/tc-i386.c
>> @@ -5409,7 +5409,7 @@ ginsn_dw2_regnum (const reg_entry *ireg)
>>     if (ireg->reg_num == RegIP || ireg->reg_num == RegIZ)
>>       return GINSN_DW2_REGNUM_RSI_DUMMY;
>>   
>> -  dwarf_reg = ireg->dw2_regnum[flag_code >> 1];
>> +  dwarf_reg = ireg->dw2_regnum[object_64bit];
>>   
>>     if (dwarf_reg == Dw2Inval)
>>       {
>> @@ -17461,7 +17461,7 @@ tc_x86_parse_to_dw2regnum (expressionS *
>>         if ((addressT) exp->X_add_number < i386_regtab_size)
>>   	{
>>   	  exp->X_add_number = i386_regtab[exp->X_add_number]
>> -			      .dw2_regnum[flag_code >> 1];
>> +			      .dw2_regnum[object_64bit];
>>   	  if (exp->X_add_number != Dw2Inval)
>>   	    exp->X_op = O_constant;
>>   	}
> 
> On one hand, I see that the suggested code changes are making things 
> semantically clearer, I would like to understand:
> 
> 1. If there is a scenario where flag_code is CODE16_BIT / CODE32_BIT and 
> object_64bit equal to 1 is supported.  gcc passes --32 when using -m16 
> or -m32.

Well, gcc may never produce such input, but hand-written assembly can.

> 2. Irrespective of #1, shouldn't we then also use "if (object_64bit == 
> 1)" instead of "if (flag_code == CODE_64BIT)" in md_begin where we set 
> the value of x86_dwarf2_return_column etc ?

Good point, let me make a v2.

Jan